Quantifying changes in the low-frequency dynamics of amorphous polymers by 2D correlation mechanical spectroscopy.

The journal of physical chemistry. B

PubMedID: 23234456

Wu X, Wang H, Zhu Z, Liu CS. Quantifying changes in the low-frequency dynamics of amorphous polymers by 2D correlation mechanical spectroscopy. J Phys Chem B. 2013;117(1):467-72.
The longer segmental dynamics of sub-Rouse modes in polystyrene with different molecular weights has been investigated by 2D correlation mechanical spectroscopy. The sub-Rouse modes were first separated from the a relaxation and Rouse modes, and their dynamics exhibits a similar change at the same temperature, T(B) ˜ 1.2T(g), as the a relaxation. The relaxation time of sub-Rouse modes at T(B) is independent of molecular weight and has a value of about 0.1 s, indicating that solely the time scale of the relaxation determines the change in dynamics of sub-Rouse modes. According to the coupling model, the change is caused by a strong increase in intermolecular cooperativity. The present work provides direct evidence for the intermolecular coupled nature of the sub-Rouse modes and demonstrates that the properties of the sub-Rouse modes resemble those of a relaxation, which could provide a new perspective for understanding the glass transition of polymers.